J Neurosurg 75:378-381, 1991
The relationship between intelligence and memory following minor or mild closed head injury: greater impairment in memory than intelligence STUART HALL, PH.D., AND ROBERT A. BORNSTE1N, PH.D.
Department qf P.~y~hiatry and Division qf Health Psychology. Ohio State University College of Medicine, Columbus. Ohio
u, This sludy investigated the performance of patients with minor or mild closed head injury and age/ education-matched normal controls on the Wechsler Adult Intelligence Scale-Revised (WAIS-R) and the Wechsler Memory Scale-Revised(WMS-R). The results demonstrated that the control group had significantly higher scores than the patients with closed head injury on all WAIS-R and WMS-R index scores. Further analysis revealed that the patients with closed head injury showed a greater impairment in delayed memory when directly compared to intellectual performance that was not seen in the control group. These results are discussed in relation to findings in patients with more severe closed head injury, the construction of the WAISR and the WMS-R, and the performance patterns of the two groups. KEY WORDS
"
closed head injury
T has been well established that the sequelae of closed head injury include impairment in intellectual ability and memory function. ~'4s'~'~3'lS'jy'~s However, the relationship between memory deficits and intellectual impairment following closed head injury is not well understood. Relatively few studies have simultaneously measured intelligence (IQ) and memory in patients with closed head injury, and even fewer have attempted to delineate dissociations between the two. Levin, et al.,'2 investigated IQ and memory in patients with moderate or severe head injury whose intellectual scores were in the normal range. They found that these patients showed a disproportionate impairment in memory at both 5 to 15 months and 16 to 42 months after head injury. These findings were cited as evidence that memory impairment may persist in spite of recovery of relatively normal intellectual function following closed head injury. However, they also noted that patients with memory impairment tended to have lower intellectual performance than patients whose memory was unimpaired. Stuss, et al., ~s found that closed headinjured patients with "good recovery" did worse on a delayed memory task than control individuals who were matched on Full-Scale IQ testing. A major limitation in these studies has been the inability to draw direct comparisons between scores on memory and intellectual measures. The recent devel-
I
378
9 intelligence
9 memory
opment of the Wechsler Memory Scale-Revised (WMSR), however, provides an opportunity to make such comparisons. 19 The WMS-R contains five specific indexes that are derived with the same psychometric properties (mean + standard deviation (SD) = 100 _+ 15) as the Verbal IQ, Performance IQ, and Full-Scale IQ of the Wechsler Adult Intelligence Scale-Revised (WAIS-R)) ~ Because of their similar psychometric properties, direct comparisons can be made between WAIS-R IQ scores and WMS-R Index scores within and between groups. Bornstein, et aL, ~ used this approach to investigate IQ/ memory discrepancies from the WAIS-R and WMS-R in normal individuals and in a heterogeneous clinical sample with diagnoses likely to be associated with memory dysfunction. They found that the discrepancy in score between Full-Scale IQ and the Delayed Memory Index was significantly different for the two groups, but material-specific discrepancies between IQ scores and immediate-recall memory scores (Verbal IQ-Verbal Memory Index; Performance IQ-Visual Memory Index) were not. The present study was designed to concurrently evaluate the performance of patients with closed head injury and normal control individuals on the WAIS-R and the WMS-R. The relationship of the scores on memory and intellectual measures within each group and how J. Neurosurg. / Volume 75/September, 1991
Memory and intelligence after minor closed head injury TABLE 1
Mean age, education, WAIS-R IQ scores and WMS-R Index scores for minor or mild closed head injury and control subjects* Variable age (yrs) education (yrs) Full-ScalelQ VerballQ Performance 1Q GeneralMemory Attention/ Concentration Verbal Memory VisualMemory Delayed Memory
Head-Injured Group 34.32 _+ 13.29 14.64 -+ 2.28 97.18+ 13.41 98.18___ 13.15 96.86_+13.32 95.14_+17.48 96.18 +_ 17.95
Control Group
Significance t
32.36 _ 12.18 -0,51 15.04 + 1.76 0.67 109.41 +9.31 3.51 108.04+9.24 2.88 109.73 _ 12.48 3.31 118.78 _+ 10.33 5.46 105.68 _ I0.81 2.13
95.41 _+ 16.70 115.50 - 10.23 96.82+ 18.96 113.32 _+9.71 92.04+ 19.10 118.77_+ 11.49
p ns ns 0.001 0.006 0.002 0.001 0.04
4.81 0.001 3.63 0.001 5.62 0,001
* WAIS-R = Wechsler Adult Intelligence Scale-Revised; IQ = intelligence quotient; WMS-R = Wechsler Memory Scale-Revised; ns = not significam.
it differed between the groups was of particular interest. Patients with minor or mild closed head injury were used in this study to determine the effects of less-severe closed head injury on intellectual and memory abilities and to allow for comparison with previous studies using patients with severe closed head injury. Study Methods and Results
Study Subjects The subjects consisted of 22 patients with closed head injury and 22 normal control individuals who were administered the WMS-R and the WAIS-R as part of a complete neuropsychological evaluation at the Ohio State University. The normal control volunteers were recruited by advertisements in local newspapers and were paid for their participation. They had no history of substance abuse, psychiatric illness, or neurological disease. The groups were matched (Table 1), so that they were not significantly different in respect to age (t(42) = -0.51), level of education (t(42) = 0.67), or sex (closed head injury group: 14 men and eight women, control group: 10 men and 12 women; x z = 1.47, not significant). Among the patients with closed head injury, 19% suffered skull fractures and 19% had hematomas. In terms of posttraumatic amnesia and retrograde amnesia, 73% of the patients with closed head injury had no posttraumatic amnesia or retrograde amnesia at the time of neuropsychological evaluation (minor closed head injury) and the remaining 27% had posttraumatic amnesia of less than 30 minutes' duration (mild closed head injury). 1"2 Retrograde amnesia was present in 14% of the closed head injury subjects, but in none of these subjects did it exist for more than 24 hours. The mean time (_+ SD) from injury to neuropsychological examination for the closed head injury group was 12.8 _+ 22.6 months (median 2 months, range 92 months). Of the closed head injury group, J. Neurosurg. / Volume 75/September, 1991
71.5% were evaluated within 6 months of injury, 19% between 1 and 2 years postinjury, and 9.5% after 2 years postinjury.
WAIS-R IQ and WMS-R Index Scores The mean scores + SD of the WAIS-R IQ and WMSR Indexes of the closed head injury patients and normal control individuals are shown in Table 1. In order to evaluate the effects of closed head injury, on memory and intellectual function, these scores were analyzed by multivariate analysis of variance (MANOVA). The Full-Scale IQ and General Memory Index were not included in this analysis because they represent composites of other variables included in the analysis and therefore are not independent. The MANOVA yielded a significant overall multivariate group effect (F(1,42) = 24.42, p < 0.001) and a significant group X test interaction (F(1,43) = 3.79, p < 0.001). Inspection of Table 1 indicates that the source of the interaction is the relatively greater deficits of the closed head injury patients on the Verbal Memory Index, Visual Memory Index, and Delayed Memory Index. In order to compare the groups on the individual IQ and Index scores, t-tests were conducted. These comparisons showed that the patients with closed head injury and the normal control individuals were significantly different on all IQ scores and memory indexes (see Table 1). D~erential Performance on WAIS-R IQ and W3IS-R Index Scores Although the closed head injury patients and normal control volunteers were significantly different on all variables noted above, the relationship between the groups' performance on intellectual measures and memory tasks also appeared to be different. For example, the mean Delayed Memory Index score for the normal controls was somewhat greater than their mean FullScale IQ score, while the mean Delayed Memory Index score for the closed head injury patients was somewhat lower than their mean Full-Scale IQ score. Other work has shown that discrepancy scores between Full-Scale IQ and the Delayed Memory Index best differentiated normal subjects from a clinical sample with disorders associated with memory deficits. 6 Therefore, we decided to investigate the relationship between the Full-Scale IQ and Delayed Memory Index scores of the two groups in the present study. A second MANOVA (with FullScale IQ and Delayed Memory Index as within-subject factors) was conducted that revealed significant group X test interaction (F(1,42) = 15.00, p < 0.001), and a significant effect for group (F(1,42) = 27.41, p < 0.001) (Fig. 1). In order to explore the potential influence of duration between closed head injury and assessment, the discrepancy score between Full-Scale IQ and Delayed Memory Index (Full-Scale IQ-Delayed Memory Index) for the closed head injury group was correlated with duration of illness. The Pearson r correlation between the dis379
S. Hall and R. A. Bornstein
FIG. 1. Mean Full-ScaleIntelligence Quotient (FSIQ) and Delayed Memory Index (DMI) for control subjects and patients with minor or mild closed head injury (CHI). Note the relatively higher DM1 scores than FSIQ for control subjects, while the opposite pattern is present for patients with dosed head injury.
crepancy score and the length of time from closed head injury to neuropsychological assessment was not significant (r -- -0.22) and accounted for less than 5% of the variance.
Discussion The results of this study indicate that minor or mild closed head injury produces a disproportionately greater impairment in delayed memory when directly compared to intellectual function. Although the patients with closed head injury had a significantly lower FullScale IQ than the normal control subjects, they showed an even greater impairment on the Delayed Memory Index. This finding is consistent with previous studies on patients with more severe injuries and suggests that the disproportionate effect of closed head injury on memory is present in milder degrees of closed head injury? 2,'8 It has been shown that educational level is highly correlated with performance on IQ measures? '9'~+ Because the patients and normal control subjects in this study were matched for educational level, it is unlikely that the significant difference between the groups in Full-Scale IQ reflects a pre-existing difference. Rather, it appears that this finding is indicative of the detrimental effects of minor or mild closed head injury on FullScale IQ. It is noteworthy that the patients had a mean Full-Scale IQ in the average range (98.26), emphasizing the fact that IQ scores in this range (particularly in welleducated individuals such as in the present study) may not reflect normal intellectual ability following closed head injury. It is interesting that the normal control subjects in the present study had a mean Delayed Memory Index score (118.77) substantially greater than their mean Full-Scale IQ (109.41). This raises the question of whether higher scores on the WMS-R Indexes when compared to WAIS-R IQ scores are typical of normal subjects. Butters, et at., 7 found that normal control individuals with a mean age and educational level of 50.60 and 16.27 years, respectively, had a mean De380
layed Memory Index of 125.87. Unfortunately, scores on intellectual measures were not reported for these subjects so that direct comparisons between performance on memory and intellectual tests are not possible. Nevertheless, it is interesting to note that, in the present study, normal control subjects had higher Delayed Memory Index scores than their Full-Scale IQ scores while, for the patients with closed head injury, the reverse was true. The finding that Full-Scale IQ is less affected than delayed memory after closed head injury may reflect the different composition of the Full-Scale IQ and Delayed Memory Index. The Full-Scale IQ is a composite score derived from a patient's performance on six verbal subtests and five performance subtests of the WAIS-R and is designed to measure a patient's global intelligence. Several verbal subtests (Information, Comprehension, Vocabulary) have been shown to be more resistant to the effects of brain damage because they measure "crystallized" or well-established overlearned aspects of intelligence.3'L~ The fact that these less sensitive verbal subtests contribute to the Full-Scale IQ may serve to keep these scores in a more "normal" range. On the other hand, memory dysfunction is a common complaint following closed head injury, and the Delayed Memory Index is the most sensitive measure of general memory dysfunction in the WMS-R. + Memory performance by definition requires new learning or "fluid" abilities. T M As a result, the Delayed Memory Index does not contain a crystallized component that might serve to make these scores resistant to the effects of closed head injury. Thus, on the basis of the composition and sensitivity of the tests, one might expect to see a somewhat lower Delayed Memory Index score than Full-Scale IQ after closed head injury. It should be emphasized that comparison of FullScale IQ and Delayed Memory Index scores in isolation is not sufficient to adequately characterize differential impairments. Clinical judgments regarding the presence of memory deficits (or any other deficit) must include evaluation of a number of aspects of performance. However, comparing the Full-Scale IQ and Delayed Memory Index score does appear to be useful for making judgments about the relative impairment of memory and intellectual abilities following minor or mild closed head injury. The present study demonstrates that the findings of previous research showing greater impairment in memory than intellectual function following severe closed head injury is also seen in patients with less severe closed head injury. However, these findings should be viewed with caution because of the small sample size. The majority of patients (71.5%) in the present study were evaluated in the early stages of recovery from closed head injury. Thus, it remains to be seen if the disproportionate impairment in memory is a chronic effect. The nonsignificant correlation between the discrepancy score (Full-Scale IQ-Delayed Memory Index) and duration from injury suggests that this may be the J. Neurosurg. / Volume 75/September, 1991
Memory and intelligence after minor closed head injury case. However, this must be considered tentative because of the small number of subjects with longer durations. Further studies with larger numbers of patients will be needed to confirm these results. The fact that the WAIS-R and the WMS-R have been developed with the same psychometric properties should facilitate investigations comparing intellectual and memory performance in various patient populations. Future research involving longitudinal studies of patients with minor or mild closed head injury as well as other populations (patients with conditions other than closed head injury) with memory dysfunction on the WAIS-R and WMS-R would be of particular interest. References 1. Barth JT, Macciocchi SN, Giordani B, etal: Neuropsychological sequelae of minor head injury. Neurosurgery 13:529-533, 1983 2. Becker DP, Grossman RG, McLaurin RL, et al: Head injuries- panel 3. Arch Neurol 36:750-758, 1979 3. Bigler ED: Diagnostic Clinical Neuropsychology. Austin: University of Texas Press, 1988 4. Bigler ED, Steinman DS, Newton JS: Clinical assessment of cognitive deficit in neurologic disorder. I1. Cerebral trauma. Clin Neuropsychol 3:13-18, 1981 5. Bornstein RA: Relationship of age and education to neuropsychological performance in patients with symptomatic carotid artery disease. J Clin Psychul 39:470-478, 1983 6. Bornstein RA, Chelune G J, Prifitera A: IQ-memory discrepancies in normal and clinical samples. Psychol Assess 1:203-206, 1989 7. Butters N, Salmon DP, Cullum CM, et al: Differentiation of amnesic and demented patients with the Wechsler Memory Scale-Revised. Clin Neuropsychologist 2: 133-148, 1988 8. Dikmen S, Temkin N, Mclean A, etal: Memory and head injury severity. J Neurol Neurosurg Psychiatry 50: 1613-1618, 1987 9. Finlayson MAJ, Johnson KA, Reitan RM: Relationship
J. Neurosurg. / Volume 75/September, 1991
10. 11. 12.
13. 14. 15.
16. 17. 18. 19. 20.
of level of education to neuropsychological measures in brain-damaged and non-brain-damaged adults, d Consult Clin Psycho145:536-542, 1977 Horn JL, Cattell RB: Age differences in fluid and crystallized intelligence. Acta Psychobiol 26:107-129, 1967 Levin HS, Benton AL, Grossman RG: Neurobehavioral Consequences of Closed Head Injury. New York: Oxford University Press, 1982 Levin HS, Goldstein FC, High WM: Disproportionately severe memory deficit in relation to normal intellectual functioning after closed head injury, d Neurol Neurosurg Psychiatry 51:1294-130 l, 1988 Levin HS, Grossman RG: Behavioral sequelae of closed head injury. Arch Neurol 35:720-727, 1978 Matarazzo JD, Herman DO: Relationship of education and IQ in the WAIS-R standardized sample. J Consult Clin Psychol 52:631-634, 1984 Newcombe F, Ratcliff G: Long-term psychological consequences of cerebral lesions, in Gazzaniga MS (ed): Handbook of Behavioral Neurobiology. Vol 2. Neuropsychology. New York: Plenum Press, 1979 Russell EW: Three patterns of brain damage on the WAIS. J Clin Psychol 35:611-620, 1979 Schacter DL, Crovitz HF: Memory function after closed head injury: a review of the quantitative research. Cortex 8:150-176, 1977 Stuss DT, Ely P, Hugenholtz H, el al: Subtle neuropsychological deficits in patients with good recovery after closed head injury. Neurosurgery 17:41-46, 1985 Wechsler D: Manual for the Wechsler Memory ScaleRevised. San Antonio, Tex: The Psychological Corporalion, 1987 Wechsler D: Wechsler Adult Intelligence Scale-Revised. New York: The Psychological Corporation, 1981
Manuscript received July 17, 1990. Accepted in final form February 21, 1991. Address reprint requests to: R. A. Bornstein, Ph.D., Neuropsychology Laboratory, Department of Psychiatry, Ohio State University, 473 West 12th Avenue, Columbus, Ohio 43210.
381
The relationship between intelligence and memory following minor or mild closed head injury: greater impairment in memory than intelligence STUART HALL, PH.D., AND ROBERT A. BORNSTE1N, PH.D.
Department qf P.~y~hiatry and Division qf Health Psychology. Ohio State University College of Medicine, Columbus. Ohio
u, This sludy investigated the performance of patients with minor or mild closed head injury and age/ education-matched normal controls on the Wechsler Adult Intelligence Scale-Revised (WAIS-R) and the Wechsler Memory Scale-Revised(WMS-R). The results demonstrated that the control group had significantly higher scores than the patients with closed head injury on all WAIS-R and WMS-R index scores. Further analysis revealed that the patients with closed head injury showed a greater impairment in delayed memory when directly compared to intellectual performance that was not seen in the control group. These results are discussed in relation to findings in patients with more severe closed head injury, the construction of the WAISR and the WMS-R, and the performance patterns of the two groups. KEY WORDS
"
closed head injury
T has been well established that the sequelae of closed head injury include impairment in intellectual ability and memory function. ~'4s'~'~3'lS'jy'~s However, the relationship between memory deficits and intellectual impairment following closed head injury is not well understood. Relatively few studies have simultaneously measured intelligence (IQ) and memory in patients with closed head injury, and even fewer have attempted to delineate dissociations between the two. Levin, et al.,'2 investigated IQ and memory in patients with moderate or severe head injury whose intellectual scores were in the normal range. They found that these patients showed a disproportionate impairment in memory at both 5 to 15 months and 16 to 42 months after head injury. These findings were cited as evidence that memory impairment may persist in spite of recovery of relatively normal intellectual function following closed head injury. However, they also noted that patients with memory impairment tended to have lower intellectual performance than patients whose memory was unimpaired. Stuss, et al., ~s found that closed headinjured patients with "good recovery" did worse on a delayed memory task than control individuals who were matched on Full-Scale IQ testing. A major limitation in these studies has been the inability to draw direct comparisons between scores on memory and intellectual measures. The recent devel-
I
378
9 intelligence
9 memory
opment of the Wechsler Memory Scale-Revised (WMSR), however, provides an opportunity to make such comparisons. 19 The WMS-R contains five specific indexes that are derived with the same psychometric properties (mean + standard deviation (SD) = 100 _+ 15) as the Verbal IQ, Performance IQ, and Full-Scale IQ of the Wechsler Adult Intelligence Scale-Revised (WAIS-R)) ~ Because of their similar psychometric properties, direct comparisons can be made between WAIS-R IQ scores and WMS-R Index scores within and between groups. Bornstein, et aL, ~ used this approach to investigate IQ/ memory discrepancies from the WAIS-R and WMS-R in normal individuals and in a heterogeneous clinical sample with diagnoses likely to be associated with memory dysfunction. They found that the discrepancy in score between Full-Scale IQ and the Delayed Memory Index was significantly different for the two groups, but material-specific discrepancies between IQ scores and immediate-recall memory scores (Verbal IQ-Verbal Memory Index; Performance IQ-Visual Memory Index) were not. The present study was designed to concurrently evaluate the performance of patients with closed head injury and normal control individuals on the WAIS-R and the WMS-R. The relationship of the scores on memory and intellectual measures within each group and how J. Neurosurg. / Volume 75/September, 1991
Memory and intelligence after minor closed head injury TABLE 1
Mean age, education, WAIS-R IQ scores and WMS-R Index scores for minor or mild closed head injury and control subjects* Variable age (yrs) education (yrs) Full-ScalelQ VerballQ Performance 1Q GeneralMemory Attention/ Concentration Verbal Memory VisualMemory Delayed Memory
Head-Injured Group 34.32 _+ 13.29 14.64 -+ 2.28 97.18+ 13.41 98.18___ 13.15 96.86_+13.32 95.14_+17.48 96.18 +_ 17.95
Control Group
Significance t
32.36 _ 12.18 -0,51 15.04 + 1.76 0.67 109.41 +9.31 3.51 108.04+9.24 2.88 109.73 _ 12.48 3.31 118.78 _+ 10.33 5.46 105.68 _ I0.81 2.13
95.41 _+ 16.70 115.50 - 10.23 96.82+ 18.96 113.32 _+9.71 92.04+ 19.10 118.77_+ 11.49
p ns ns 0.001 0.006 0.002 0.001 0.04
4.81 0.001 3.63 0.001 5.62 0,001
* WAIS-R = Wechsler Adult Intelligence Scale-Revised; IQ = intelligence quotient; WMS-R = Wechsler Memory Scale-Revised; ns = not significam.
it differed between the groups was of particular interest. Patients with minor or mild closed head injury were used in this study to determine the effects of less-severe closed head injury on intellectual and memory abilities and to allow for comparison with previous studies using patients with severe closed head injury. Study Methods and Results
Study Subjects The subjects consisted of 22 patients with closed head injury and 22 normal control individuals who were administered the WMS-R and the WAIS-R as part of a complete neuropsychological evaluation at the Ohio State University. The normal control volunteers were recruited by advertisements in local newspapers and were paid for their participation. They had no history of substance abuse, psychiatric illness, or neurological disease. The groups were matched (Table 1), so that they were not significantly different in respect to age (t(42) = -0.51), level of education (t(42) = 0.67), or sex (closed head injury group: 14 men and eight women, control group: 10 men and 12 women; x z = 1.47, not significant). Among the patients with closed head injury, 19% suffered skull fractures and 19% had hematomas. In terms of posttraumatic amnesia and retrograde amnesia, 73% of the patients with closed head injury had no posttraumatic amnesia or retrograde amnesia at the time of neuropsychological evaluation (minor closed head injury) and the remaining 27% had posttraumatic amnesia of less than 30 minutes' duration (mild closed head injury). 1"2 Retrograde amnesia was present in 14% of the closed head injury subjects, but in none of these subjects did it exist for more than 24 hours. The mean time (_+ SD) from injury to neuropsychological examination for the closed head injury group was 12.8 _+ 22.6 months (median 2 months, range 92 months). Of the closed head injury group, J. Neurosurg. / Volume 75/September, 1991
71.5% were evaluated within 6 months of injury, 19% between 1 and 2 years postinjury, and 9.5% after 2 years postinjury.
WAIS-R IQ and WMS-R Index Scores The mean scores + SD of the WAIS-R IQ and WMSR Indexes of the closed head injury patients and normal control individuals are shown in Table 1. In order to evaluate the effects of closed head injury, on memory and intellectual function, these scores were analyzed by multivariate analysis of variance (MANOVA). The Full-Scale IQ and General Memory Index were not included in this analysis because they represent composites of other variables included in the analysis and therefore are not independent. The MANOVA yielded a significant overall multivariate group effect (F(1,42) = 24.42, p < 0.001) and a significant group X test interaction (F(1,43) = 3.79, p < 0.001). Inspection of Table 1 indicates that the source of the interaction is the relatively greater deficits of the closed head injury patients on the Verbal Memory Index, Visual Memory Index, and Delayed Memory Index. In order to compare the groups on the individual IQ and Index scores, t-tests were conducted. These comparisons showed that the patients with closed head injury and the normal control individuals were significantly different on all IQ scores and memory indexes (see Table 1). D~erential Performance on WAIS-R IQ and W3IS-R Index Scores Although the closed head injury patients and normal control volunteers were significantly different on all variables noted above, the relationship between the groups' performance on intellectual measures and memory tasks also appeared to be different. For example, the mean Delayed Memory Index score for the normal controls was somewhat greater than their mean FullScale IQ score, while the mean Delayed Memory Index score for the closed head injury patients was somewhat lower than their mean Full-Scale IQ score. Other work has shown that discrepancy scores between Full-Scale IQ and the Delayed Memory Index best differentiated normal subjects from a clinical sample with disorders associated with memory deficits. 6 Therefore, we decided to investigate the relationship between the Full-Scale IQ and Delayed Memory Index scores of the two groups in the present study. A second MANOVA (with FullScale IQ and Delayed Memory Index as within-subject factors) was conducted that revealed significant group X test interaction (F(1,42) = 15.00, p < 0.001), and a significant effect for group (F(1,42) = 27.41, p < 0.001) (Fig. 1). In order to explore the potential influence of duration between closed head injury and assessment, the discrepancy score between Full-Scale IQ and Delayed Memory Index (Full-Scale IQ-Delayed Memory Index) for the closed head injury group was correlated with duration of illness. The Pearson r correlation between the dis379
S. Hall and R. A. Bornstein
FIG. 1. Mean Full-ScaleIntelligence Quotient (FSIQ) and Delayed Memory Index (DMI) for control subjects and patients with minor or mild closed head injury (CHI). Note the relatively higher DM1 scores than FSIQ for control subjects, while the opposite pattern is present for patients with dosed head injury.
crepancy score and the length of time from closed head injury to neuropsychological assessment was not significant (r -- -0.22) and accounted for less than 5% of the variance.
Discussion The results of this study indicate that minor or mild closed head injury produces a disproportionately greater impairment in delayed memory when directly compared to intellectual function. Although the patients with closed head injury had a significantly lower FullScale IQ than the normal control subjects, they showed an even greater impairment on the Delayed Memory Index. This finding is consistent with previous studies on patients with more severe injuries and suggests that the disproportionate effect of closed head injury on memory is present in milder degrees of closed head injury? 2,'8 It has been shown that educational level is highly correlated with performance on IQ measures? '9'~+ Because the patients and normal control subjects in this study were matched for educational level, it is unlikely that the significant difference between the groups in Full-Scale IQ reflects a pre-existing difference. Rather, it appears that this finding is indicative of the detrimental effects of minor or mild closed head injury on FullScale IQ. It is noteworthy that the patients had a mean Full-Scale IQ in the average range (98.26), emphasizing the fact that IQ scores in this range (particularly in welleducated individuals such as in the present study) may not reflect normal intellectual ability following closed head injury. It is interesting that the normal control subjects in the present study had a mean Delayed Memory Index score (118.77) substantially greater than their mean Full-Scale IQ (109.41). This raises the question of whether higher scores on the WMS-R Indexes when compared to WAIS-R IQ scores are typical of normal subjects. Butters, et at., 7 found that normal control individuals with a mean age and educational level of 50.60 and 16.27 years, respectively, had a mean De380
layed Memory Index of 125.87. Unfortunately, scores on intellectual measures were not reported for these subjects so that direct comparisons between performance on memory and intellectual tests are not possible. Nevertheless, it is interesting to note that, in the present study, normal control subjects had higher Delayed Memory Index scores than their Full-Scale IQ scores while, for the patients with closed head injury, the reverse was true. The finding that Full-Scale IQ is less affected than delayed memory after closed head injury may reflect the different composition of the Full-Scale IQ and Delayed Memory Index. The Full-Scale IQ is a composite score derived from a patient's performance on six verbal subtests and five performance subtests of the WAIS-R and is designed to measure a patient's global intelligence. Several verbal subtests (Information, Comprehension, Vocabulary) have been shown to be more resistant to the effects of brain damage because they measure "crystallized" or well-established overlearned aspects of intelligence.3'L~ The fact that these less sensitive verbal subtests contribute to the Full-Scale IQ may serve to keep these scores in a more "normal" range. On the other hand, memory dysfunction is a common complaint following closed head injury, and the Delayed Memory Index is the most sensitive measure of general memory dysfunction in the WMS-R. + Memory performance by definition requires new learning or "fluid" abilities. T M As a result, the Delayed Memory Index does not contain a crystallized component that might serve to make these scores resistant to the effects of closed head injury. Thus, on the basis of the composition and sensitivity of the tests, one might expect to see a somewhat lower Delayed Memory Index score than Full-Scale IQ after closed head injury. It should be emphasized that comparison of FullScale IQ and Delayed Memory Index scores in isolation is not sufficient to adequately characterize differential impairments. Clinical judgments regarding the presence of memory deficits (or any other deficit) must include evaluation of a number of aspects of performance. However, comparing the Full-Scale IQ and Delayed Memory Index score does appear to be useful for making judgments about the relative impairment of memory and intellectual abilities following minor or mild closed head injury. The present study demonstrates that the findings of previous research showing greater impairment in memory than intellectual function following severe closed head injury is also seen in patients with less severe closed head injury. However, these findings should be viewed with caution because of the small sample size. The majority of patients (71.5%) in the present study were evaluated in the early stages of recovery from closed head injury. Thus, it remains to be seen if the disproportionate impairment in memory is a chronic effect. The nonsignificant correlation between the discrepancy score (Full-Scale IQ-Delayed Memory Index) and duration from injury suggests that this may be the J. Neurosurg. / Volume 75/September, 1991
Memory and intelligence after minor closed head injury case. However, this must be considered tentative because of the small number of subjects with longer durations. Further studies with larger numbers of patients will be needed to confirm these results. The fact that the WAIS-R and the WMS-R have been developed with the same psychometric properties should facilitate investigations comparing intellectual and memory performance in various patient populations. Future research involving longitudinal studies of patients with minor or mild closed head injury as well as other populations (patients with conditions other than closed head injury) with memory dysfunction on the WAIS-R and WMS-R would be of particular interest. References 1. Barth JT, Macciocchi SN, Giordani B, etal: Neuropsychological sequelae of minor head injury. Neurosurgery 13:529-533, 1983 2. Becker DP, Grossman RG, McLaurin RL, et al: Head injuries- panel 3. Arch Neurol 36:750-758, 1979 3. Bigler ED: Diagnostic Clinical Neuropsychology. Austin: University of Texas Press, 1988 4. Bigler ED, Steinman DS, Newton JS: Clinical assessment of cognitive deficit in neurologic disorder. I1. Cerebral trauma. Clin Neuropsychol 3:13-18, 1981 5. Bornstein RA: Relationship of age and education to neuropsychological performance in patients with symptomatic carotid artery disease. J Clin Psychul 39:470-478, 1983 6. Bornstein RA, Chelune G J, Prifitera A: IQ-memory discrepancies in normal and clinical samples. Psychol Assess 1:203-206, 1989 7. Butters N, Salmon DP, Cullum CM, et al: Differentiation of amnesic and demented patients with the Wechsler Memory Scale-Revised. Clin Neuropsychologist 2: 133-148, 1988 8. Dikmen S, Temkin N, Mclean A, etal: Memory and head injury severity. J Neurol Neurosurg Psychiatry 50: 1613-1618, 1987 9. Finlayson MAJ, Johnson KA, Reitan RM: Relationship
J. Neurosurg. / Volume 75/September, 1991
10. 11. 12.
13. 14. 15.
16. 17. 18. 19. 20.
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Manuscript received July 17, 1990. Accepted in final form February 21, 1991. Address reprint requests to: R. A. Bornstein, Ph.D., Neuropsychology Laboratory, Department of Psychiatry, Ohio State University, 473 West 12th Avenue, Columbus, Ohio 43210.
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